Soundcraftsmen Pro-Control Three Preamplifier Review

The Soundcraftsmen Pro-Control Three preamplifier employs complementary metal-oxide-semiconductor (CMOS) digital-control electronic switching for operation free of noise and distortion. Switching is done directly at the required point in the circuit, close to the signal input and output jacks, for minimum crosstalk and noise pickup. The Pro-Control Three provides fully independent selection of program sources for listening and recording. Two square buttons step through the available sources sequentially, and parallel horizontal rows of lights (green for LISTEN, red for RECORD) show the status of the selectors.

Inputs include CD, tuner, phono, and two tape decks. Two buttons in the center of the panel are marked LOOP and DIRECT. The first controls an external-processor loop, which can be used to insert an accessory such as an equalizer into either the listening or recording signal path or bypass it entirely. The DIRECT button bypasses the tone controls and the external-processor loop, providing the shortest possible signal path through the preamplifier, from input to output.

The other panel controls are a large volume knob, with a highly visible green led index pointer, and smaller, center-detented knobs for the bass and treble tone controls and the balance control. The power switch, a square button like the signal selectors, is immediately below the stereo headphone jack.

The rear apron of the preamplifier contains twin rows of input/output jacks (the phono input jacks are gold plated) and two AC outlets, one of them switched. Its 600-watt rating far exceeds the typical rating of a preamplifier’s switched outlet (100 watts or so), giving it the ability to control the power to all the other system components, including a fairly powerful amplifier.

An unusual and convenient feature of the Soundcraftsmen Pro-Control Three is its two pairs of output jacks. In addition to the regular (normal) outputs, it has a pair of outputs of opposite polarity (inverted), which allow the preamplifier to drive almost any stereo power amplifier as if it were a bridged-mono power amp with roughly three times its normal per-channel power rating.

The made-in-California Soundcraftsmen Pro-Control Three is an attractively styled unit with a sculptured charcoal-gray front panel and exceptionally legible white markings. Optional wood side panels are available. Removing the cover revealed one of the cleanest interiors we have found in a comparably priced hi-fi component. Virtually the entire preamplifier is constructed on one circuit board; the input/output connectors are attached to its rear edge, and a display/control board is attached to the front panel and the main circuit board. Almost all of the active circuit elements are integrated circuits, the major exception being in the phono preamplifier, which consists entirely of discrete-transistor circuits. The only visible wires in the preamplifier connect the circuit board to the power supply.

The Soundcraftsmen Pro-Control Three measures 19 inches wide, 10-1/2 inches deep, and 3-1/2 inches high, and it weighs 15 pounds. Price: $549; wood side panels, $30.

Lab Tests

The frequency response of the Soundcraftsmen Pro-Control Three, measured through its CD input, varied less than 0.15 dB overall from 10 to 30.000 Hz and was down 0.5 dB at 100.000 Hz. Switching to the direct mode, bypassing the tone controls, improved the response to an impressive + 0, —0.1 dB from 10 to 100,000 Hz and ± 0.02 dB from 20 to 20,000 Hz. The phono section’s response was within ±0.4 dB of the standard RIAA equalization characteristic from 20 to 20.000 Hz.

The tone controls had excellent characteristics, with little effect on the midrange response. The treble curves were hinged at 2,500 Hz, and the maximum range was ±13 dB at 20,000 Hz. The bass control had a sliding turnover frequency, shifting from below 50 Hz to about 150 Hz over the adjustment range of the control, with a maximum effect of ±12 dB at 20 Hz.

The output of the preamplifier clipped at 8.8 volts into a high-impedance load and at 6.5 volts into 600 ohms. The total harmonic distortion (THD) plus noise was 0.02 to 0.03 percent from 1 volt output to the clipping point. The sensitivity, for a 0.5-volt reference output, was 0.122 volt through the CD input and 1.9 millivolts (mv) through the phono input. The A-weighted noise level (referred to 0.5 volt) was —95.5 dB through the CD input and -69 dB through the phono input. The phono noise proved to be largely 120-hz power-supply hum. Phono-input impedance was 45,000 ohms in parallel with 80 picofarads. The phono stage overloaded at the 1,000-Hz-equivalent inputs of 90 to 100 mv from 20 to 20,000 Hz, which is quite adequate for any turntable setup.

Comments

Ergonomically, the Soundcraftsmen Pro-Control Three is a refreshing advance over conventional audio-component design. Its control functions are exceptionally clear and logical; one could hardly ask for a simpler or more obvious front panel, yet the Pro-Control Three is one of the most full-featured preamplifiers on the market. The same logic and simplicity are evident in its internal construction, which is open and uncluttered in spite of its versatility.

In general, the measured performance of the Soundcraftsmen Pro-Control Three was essentially as rated, which is to say it’s more than good enough for the critical user. The response flatness, phono equalization, and tone-control characteristics were excellent, and the phono-overload levels, while not as high as those of a number of preamplifiers we have tested, were certainly adequate for their purpose.

The preamplifier fell short of meeting its specifications in only one respect, apparently the result of the manufacturer’s having rated its noise level using a nonstandard reference (that is, the preamplifier’s maximum output of 8 volts or so, instead of the EIA standard reference of 0.5 volt). The A-weighted hum-and-noise level we measured through the phono input, - 69 dB, while not particularly good, is probably acceptable in most cases. It resulted almost entirely from 120-Hz power-supply hum, a rare occurrence with today’s solid-state amplifiers. The hum component, at a level of about —55 dB, could be seen on an oscilloscope and heard via the speakers with the volume set near maximum. Our chief objection is to the — 97-dB rating, which appears to be grossly exaggerated if taken at face value and could be misleading if the Pro-Control Three were compared with amplifiers rated by the EIA standard. Measurement of a second unit showed that the hum level was not just a sample variation as we had at first suspected.

In actual listening use, the Soundcraftsmen Pro-Control Three was an excellent performer. Its control smoothness and quiet switching were obvious, and since few of us listen at a maximum gain setting its hum is not likely to be audible. Again on the plus side, the headphone volume available from this preamplifier was among the loudest we have found so far; it could actually generate uncomfortable levels through medium-impedance phones. Headphone users will be happy to know that they can leave their power amplifiers shut off if they have a Pro-Control Three.

Read all

Soundcraftsmen reviews

Read all